<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script type='text/javascript' src='../js/vue.js'></script>
</head>

<body>
    <!-- 
        监视属性watch
        1.当被监视的属性变化时，回调函数自动调用，进行相关操作
        2.监视属性必须存在，才能进行监视
        3.监视的两种写法：
            new Vue传入watch配置
            通过vm.$watch监视
     -->
    <div id="root">
        <h2>
            天气{{info}}
        </h2>
        <button @click='changeWeather'>切换天气</button>
    </div>
    <script>
        const vm = new Vue({
            el: '#root',
            data: {
                isHot: true
            },
            computed: {
                info() {
                    return this.isHot ? '炎热' : '凉爽'
                }
            },
            methods: {
                changeWeather() {
                    this.isHot = !this.isHot
                }
            },
            // watch: {
            //     immediate: true,
            //     isHot: {
            //         //handler()调用，isHot发生变化
            //         handler(newValue, oldValue) {
            //             console.log('isHot被修改了', newValue, oldValue)
            //         }
            //     }
            // }
        })

        //监控也可以：
        vm.$watch("isHot", {
            immediate: true,
            isHot: {
                //handler()调用，isHot发生变化
                handler(newValue, oldValue) {
                    console.log('isHot被修改了', newValue, oldValue)
                }
            }
        })
        console.log(vm);
    </script>
</body>

</html>